ArcGIS for AutoCAD field values can be standard values derived from values stored on the entity or assumed from the field's default value. Other field values may be linked to AutoCAD entity properties or are read-only tracking fields. Fields can be constrained by a coded value domain or a range domain, and they can be editable or read-only. A field can be defined as a subtype field, which manages a feature's membership within a feature layer subtype. The editing of a field can trigger the modification of a linked entity property. In the case of a subtype field, modifying the subtype also updates the AutoCAD layer property from one layer to another based on that subtype.
M-value implementation
To support the storage of m-values on polyline features in ArcGIS for AutoCAD, the software uses available ArcGIS for AutoCAD entities and their geometry. M-values in ArcGIS for AutoCAD require a linear entity type that has VERTEX subentities. ArcGIS for AutoCAD 2D and 3D polyline features are the only linear entity types that have VERTEX subentities. To support the creation and editing of m-values, polyline features must be drawn as 2D or 3D polyline entities. In most Autodesk AutoCAD implementations, the default linear feature is light weight polylines. In ArcGIS for AutoCAD, you can change this using the PLINETYPE system variable by changing its setting to 0 to designate 2D or 3D polylines as the default polyline entity type compatible with m-values in ArcGIS for AutoCAD. You can access and edit the m-values using the Attribute Editor user interface on linear features that have the supporting VERTEX subentity geometry such as 2D and 3D POLYLINE entities.
Web feature layers
Storing m-values on a web feature layer is a property setting of the web layer. Polyline web features that support m-values can be added to ArcGIS for AutoCAD. Features with null m-values are automatically drawn as full polylines with vertex subentities. However, features with null values are drawn according to the PLINETYPE setting. You cannot add m-values unless the PLINETYPE system variable is set to 0 to ensure that full polylines with VERTEX subentities are drawn. You cannot add m-values to features that are added to the drawing from a supported web feature layer using light weight polylines. To view or edit m-values on these features, first discard all edits; then, change the AutoCAD PLINETYPE system variable to 0, and re-add the web feature layer.
Document feature layers
By default, all linear document feature layers support adding m-values. When sharing polyline document feature layers as hosted feature layers, any included m-values will be retained. As with web feature layers, linear features of a document feature layer must be drawn with AutoCAD geometry that supports VERTEX subentities such as a 2D or 3D POLYINE entity.